We propose to add an additional aim that will expand the scope of the parent grant and increase the tempo of research by exploiting the synergy of approaches in two model systems, Drosophila and mouse C2C12 myoblast tissue culture to find basic mechanisms driving myoblast fusion. It will also allow the retention of two key personnel in my laboratory, whose outside funding will lapse in June 2009. The debilitating onset of muscle wasting, which affects mobility and quality of life, is an ever- growing problem in public health. Muscle wasting is the result of diseases such as muscular dystrophy, a side effect of chemotherapy for cancers and a hallmark of aging. Since the normal pathway to repair damaged skeletal muscles involves the fusion of satellite cells to damaged myotubes, an important step in developing treatments will be to understand the genes and mechanisms that regulate myoblast fusion. Our long-term goal is to understand essential, conserved genes and mechanisms driving myoblast fusion. Our central hypothesis in our proposal is that specific cytoskeletal rearrangements are critical for all myoblast fusions. Our strong preliminary results in the satellite cell-derived C2C12 mouse myoblast culture system indicate that certain elements of the fusion machinery are conserved across species: knockdown of 5 mammalian homologs of fly fusion genes show a myoblast fusion phenotype in C2C12 myoblasts. Guided by these strong preliminary results, we hypothesize that the paradigm of actin based activities and actin regulators that we have defined in Drosophila apply in a mammalian system. To test this hypothesis, in aim 4A, we will analyze this subset of mammalian homologs using assays that we have developed to define what aspects of the fusion process are aberrant in these knockdown lines. In aim 4B, we will determine if other homologs of fly fusion genes and if other actin regulators similarly affect fusion. Our work is significant because it is expected to reveal the essential cellular and molecular mechanisms underlying cell-cell fusion. The proposed research is relevant to public health because once the molecular players and the cellular targets of their action are identified or understood, therapies designed to regulate myoblast fusion can be developed to promote fusion for the treatment of muscle wasting due to aging or disease. PUBLIC HEALTH RELEVANCE: Critical to our understanding of muscle disease is the identification of genes and mechanisms underlying myoblast fusion. An essential model of myoblast fusion will be developed using the strengths of two model systems, Drosophila and the mouse C2C12 myoblasts.